Earlier, however, William Petty credited dyers with a slightly different explanation of the need for these assistants. 15 Petty noted that the addition of alum or other mineral salts to the dyebath allowed fibers to better accept color.

In that explanation, the dye assistants added to the dyebath removed an outer layer of the fiber during the dye process. reference This brightened the final color, much as removing the gummy, varnish-like outer coating on silk made that fiber brighter and easier to dye. reference